1. Field of the Invention
The present invention relates to an electronic device, and is particularly concerned with an electronic device with a semiconductor device mounted on a thin flexible substrate.
2. Description of the Prior Art
An ultrathin IC card 0.76 mm or so in thickness is provided hitherto as such electronic device. A conventional wire bonding system and a so-called tape assembly system (or TAB - tape automated bonding otherwise) using a flexible organic insulating film are employed for mounting a semiconductor device used on the IC card. The tape assembly system is advantageous of realizing a thinner package mounting and automation. Various modes are conceivable for mounting the semiconductor device according to the tape assembly system.
FIG. 4 is a sectional view showing a structure of a prior art semiconductor device for IC card.
In the drawing, a protuberant electrode 2 is formed on the front side surface la of a semiconductor element 1. A flexible organic insulating film 30 consisting of polyimide resin, glass epoxy resin and the like has an opening 31, and a circuit wiring 32 and an external electrode 33 of the semiconductor device which is connected electrically to one end of the circuit wiring 32 are formed on the front side surface 30a of the flexible organic insulating film 30. A lead terminal 34 is connected electrically to the other end of the circuit wiring 32, and the lead terminal 34 overhangs the opening 31. The flexible organic insulating film 30, the circuit wiring 32, the external electrode 33 and the lead terminal 34 constitute a package substrate 300. The semiconductor element 1 is disposed to position on a side of the rear side surface 30b of the flexible organic insulating film 30 under the opening 31 of the package substrate 300. The lead terminal 34 is disposed so as to come on the protuberant electrode 2, and the lead terminal 34 is connected electrically and mechanically to the protuberant electrode 2. A part of the semiconductor element 1, the protuberant electrode 2, the lead terminal 34, a part of the circuit wiring 32 and the opening 31 are sealed with a sealing resin 40 such as epoxy resin or the like. The sealing resin 40 prevents the semiconductor element 1 and others from being contaminated externally and influenced mechanically.
FIG. 5 is a sectional view showing a construction of a conventional IC card.
In the drawing, a recess 51 is formed on a front side of a flexible card 50 consisting of polyvinyl chloride resin or the like. The semiconductor device of FIG. 4 is mounted in the recess 51 with a side of the circuit wiring 32 coming on the front side of the card 50 and the front side surface 30a of the flexible organic insulating film 30 is made to coincide with the front side surface 50a of the card 50. The mounting is performed by embedding the semiconductor device in the recess 51 or by sticking the semiconductor device embedded once in the recess 51 with an adhesive to the recess 51. An overcoat film 60 about 80 .mu.m thick is formed on the front side surface of the semiconductor device and also on the front side surface 50a of the card 50 so as to flatten the front side surface of the semiconductor device. The overcoat film 60 has an opening 61 through which the external electrode 33 is exposed partly, and thus the external electrode 33 can be brought electrically into contact externally. In the example, the IC card is 0.76 mm or so in thickness, and the IC card surface must be smoothened to a flat.
Further in FIG. 4, the semiconductor device is constructed to have the semiconductor element 1 partly sealed with the sealing resin 40 is exemplified, however, such semiconductor device as is structured to have the semiconductor element 1 sealed entirely with the sealing resin including the rear side surface 1b thereof is also available otherwise.
Then, in a report titled "IC CARD: ASSEMBLY TECHNOLOGY AND RELIABILITY" by Shuji Hiranuma and 3 others at IMC 1986 Proceedings, Kobe, May 28 to 30, 1986, there given is a construction such that a semiconductor chip is fixed on a glass epoxy module substrate with TAB banp and TAB lead, and the module is mounted on a core film to a card unit.
Further, a constructional example of wire bonding system and TAB system is given as a mounting method of LSI for IC card in "IC CARD - ITS TECHNOLOGY AND SOCIAL DEVELOPMENT" issued by Nippon Industry Technology Center on Mar. 28, 1986.
Meanwhile, in a conventional IC card, the circuit wiring 32 is formed through patterning a metallic film consisting of a copper foil or the like about 35 .mu.m thick generally which is formed on the front side surface 30a of the flexible organic insulating film 30 according to photoetching or other available process, therefore a finished surface of the semiconductor device is rugged 35 .mu.m or so. For prevention a resin called solder resist is applied on the surface of the circuit wiring 32, which is still not to remove the ruggedness thoroughly. Then, since the circuit wiring 32 and the external electrode 33 are disposed on the front side surface 30a of the flexible organic insulating film 30, it is difficult to flatten the front side surface 40a of the sealing resin 40. Consequently, if the overcoat film 60 is applied after the semiconductor device is mounted on the card 50, a ruggedness on the front side surface of the semiconductor device cannot be absorbed thoroughly, thus remaining somewhat thereon. Further, the overcoat film 60 is about 80 .mu.m in thickness, therefore the semiconductor device must be thinned entirely by the thickness of the overcoat film 60 so as to obtain an IC card 0.76 mm thick, thus making the process for semiconductor device more difficult. Then, since the circuit wiring 32 is exposed on the surface of the semiconductor device, the circuit wiring 32 is still visible externally after the semiconductor device is mounted on the card 60, which is not preferable for appearance.